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From Myria <myriac...@gmail.com>
Subject Re: SHA-1 collision in repository?
Date Tue, 06 Mar 2018 03:54:22 GMT
Final email for the night >.<

What's clobbering the expanded_size is this in build_rep_list:

  /* The value as stored in the data struct.
     0 is either for unknown length or actually zero length. */
  *expanded_size = first_rep->expanded_size;

first_rep->expanded_size here is zero for the last call to this
function before the error.  In every other case before the error, the
two values are equal.

Then this code executes:

  if (*expanded_size == 0)
    if (rep_header->type == svn_fs_fs__rep_plain || first_rep->size != 4)
      *expanded_size = first_rep->size;

first_rep->size is 16384, and this is why rb->len becomes 16384,
leading to the error.

I don't know what all this code is doing, but that's the proximate
cause of the failure.

Melissa


On Mon, Mar 5, 2018 at 7:41 PM, Myria <myriachan@gmail.com> wrote:
> When Subversion gets to this part of rep_read_contents, rb->len is
> 16384.  It thinks it is then done reading the entire file, and can
> compare the checksum, but it's not done with the file yet.
>
> rb->rep.expanded_size is correct at the error point, 57465.
> rep_read_get_baton sets rb->len to rb->rep.expanded_size, so I don't
> know why the value changed by the time rep_read_contents got its paws
> on the baton.  I saw that rb->len might be getting clobbered by
> rep_read_content's call to build_rep_list, which has the following
> line of code:
>
> *expanded_size = first_rep->expanded_size;
>
> expanded_size is &rep->len.  I haven't had a chance to debug this area
> yet, so it might be fine.
>
> I verified with sqlite3 that the rep-cache.db has the correct size (57465):
>
> $ sqlite3 /mnt/d/svnclone/db/rep-cache.db "select * from rep_cache
> where hash='e6291ab119036eb783d0136afccdb3b445867364'"
> e6291ab119036eb783d0136afccdb3b445867364|227170|153|193|57465
>
>
> On Mon, Mar 5, 2018 at 6:56 PM, Myria <myriachan@gmail.com> wrote:
>> GMail keeps doing reply instead of reply all.  I'm having to manually
>> add the users list back now.
>>
>> Below is the thread I sent.
>>
>>
>> ---------- Forwarded message ----------
>> From: Myria <myriachan@gmail.com>
>> Date: Mon, Mar 5, 2018 at 6:37 PM
>> Subject: Re: SHA-1 collision in repository?
>> To: Philip Martin <philip@codematters.co.uk>
>>
>>
>> I now know where the checksum error happens, but not why.
>>
>> svn: E200014: Checksum mismatch while reading representation:
>>    expected:  bb52be764a04d511ebb06e1889910dcf
>>      actual:  80a10d37de91cadc604ba30e379651b3
>>
>> It's calculating the MD5 of only the first 16 KB of the input file and
>> comparing against the MD5 of the entire file.  The 16 KB number seems
>> to be SVN__STREAM_CHUNK_SIZE.
>>
>> bb52be764a04d511ebb06e1889910dcf is the MD5 of the entire file.
>> 80a10d37de91cadc604ba30e379651b3 is the MD5 of the first 16384 bytes.
>>
>>
>> On Mon, Mar 5, 2018 at 5:23 PM, Myria <myriachan@gmail.com> wrote:
>>> I managed to compile a subversion command line client with debugging
>>> information and optimizations disabled, and can reproduce the problem
>>> with GDB attached.
>>>
>>> Here is a backtrace at the time at which the error occurs.  A few line
>>> numbers in stream.c will be wrong by a few lines due to a few printf's
>>> I added.
>>>
>>> #0  svn_checksum_mismatch_err (expected=0x7ffffffdcf00,
>>> actual=0x7ffffa0700a0, scratch_pool=0x7ffffa070028,
>>>     fmt=0x7ffffc259ac0 "Checksum mismatch while reading
>>> representation") at subversion/libsvn_subr/checksum.c:638
>>> #1  0x00007ffffc2123de in rep_read_contents (baton=0x7ffffa1f6190,
>>>     buf=0x7ffffa1f66a8 "// <redacted>"..., len=0x7ffffffdcf88)
>>>     at subversion/libsvn_fs_fs/cached_data.c:2062
>>> #2  0x00007ffffe5645fd in svn_stream_read_full (stream=0x7ffffa1f6470,
>>>     buffer=0x7ffffa1f66a8 "// <redacted>"..., len=0x7ffffffdcf88)
>>>     at subversion/libsvn_subr/stream.c:193
>>> #3  0x00007ffffe5653f3 in svn_stream_contents_same2
>>> (same=0x7ffffffdd01c, stream1=0x7ffffa1f6470,
>>>     stream2=0x7ffffa1f6650, pool=0x7ffffa1e0028) at
>>> subversion/libsvn_subr/stream.c:589
>>> #4  0x00007ffffc247226 in get_shared_rep (old_rep=0x7ffffffdd188,
>>> fs=0x7fffff601030, rep=0x7ffffa0e20b8,
>>>     file=0x7ffffa1e0390, offset=0, reps_hash=0x0,
>>> result_pool=0x7fffff5e0028, scratch_pool=0x7ffffa1e0028)
>>>     at subversion/libsvn_fs_fs/transaction.c:2280
>>> #5  0x00007ffffc247734 in rep_write_contents_close
>>> (baton=0x7ffffa232ff0) at subversion/libsvn_fs_fs/transaction.c:2370
>>> #6  0x00007ffffe56492b in svn_stream_close (stream=0x7ffffa233140) at
>>> subversion/libsvn_subr/stream.c:274
>>> #7  0x00007ffffe841001 in apply_window (window=0x0,
>>> baton=0x7ffffa1000a0) at subversion/libsvn_delta/text_delta.c:732
>>> #8  0x00007ffffc2520d2 in window_consumer (window=0x0,
>>> baton=0x7fffff5f1ab8) at subversion/libsvn_fs_fs/tree.c:2935
>>> #9  0x00007ffffe8405ef in svn_txdelta_run (source=0x7fffff5f1a18,
>>> target=0x7fffff5f1298,
>>>     handler=0x7ffffc25209f <window_consumer>,
>>> handler_baton=0x7fffff5f1ab8, checksum_kind=svn_checksum_md5,
>>>     checksum=0x7ffffffdd458, cancel_func=0x0, cancel_baton=0x0,
>>> result_pool=0x7fffff5e0028,
>>>     scratch_pool=0x7fffff5e0028) at subversion/libsvn_delta/text_delta.c:454
>>> #10 0x00007ffffee98a57 in svn_wc__internal_transmit_text_deltas (tempfile=0x0,
>>>     new_text_base_md5_checksum=0x7ffffffdd5b0,
>>> new_text_base_sha1_checksum=0x7ffffffdd5b8, db=0x7fffff6c17d8,
>>>     local_abspath=0x7fffff672d08
>>> "/mnt/d/svntest/repository/directory/Redacted.cpp",
>>>     fulltext=0, editor=0x7fffff673700, file_baton=0x7fffff510110,
>>> result_pool=0x7fffff6c0028,
>>>     scratch_pool=0x7fffff5e0028) at subversion/libsvn_wc/adm_crawler.c:1109
>>> #11 0x00007ffffee98d68 in svn_wc_transmit_text_deltas3
>>> (new_text_base_md5_checksum=0x7ffffffdd5b0,
>>>     new_text_base_sha1_checksum=0x7ffffffdd5b8, wc_ctx=0x7fffff6c17c0,
>>>     local_abspath=0x7fffff672d08
>>> "/mnt/d/svntest/repository/directory/Redacted.cpp",
>>>     fulltext=0, editor=0x7fffff673700, file_baton=0x7fffff510110,
>>> result_pool=0x7fffff6c0028,
>>>     scratch_pool=0x7fffff5e0028) at subversion/libsvn_wc/adm_crawler.c:1199
>>> #12 0x00007fffff18eb12 in svn_client__do_commit (
>>>     base_url=0x7fffff6142c0 "file:///mnt/d/svntest/repository/directory",
>>>     commit_items=0x7fffff672c48, editor=0x7fffff673700,
>>> edit_baton=0x7fffff6300a0,
>>>     notify_path_prefix=0x7fffff672900 "/mnt/d/svntest/repository",
>>> sha1_checksums=0x7ffffffdd750,
>>>     ctx=0x7fffff6c16f0, result_pool=0x7fffff6c0028, scratch_pool=0x7fffff650028)
>>>     at subversion/libsvn_client/commit_util.c:1920
>>> #13 0x00007fffff18a5f9 in svn_client_commit6 (targets=0x7fffff670a18,
>>> depth=svn_depth_infinity, keep_locks=0,
>>>     keep_changelists=0, commit_as_operations=1,
>>> include_file_externals=0, include_dir_externals=0,
>>>     changelists=0x7fffff6c0780, revprop_table=0x0,
>>> commit_callback=0x42c6a0 <svn_cl__print_commit_info>,
>>>     commit_baton=0x0, ctx=0x7fffff6c16f0, pool=0x7fffff6c0028) at
>>> subversion/libsvn_client/commit.c:901
>>> #14 0x000000000040b744 in svn_cl__commit (os=0x7fffff6c0520,
>>> baton=0x7ffffffddc60, pool=0x7fffff6c0028)
>>>     at subversion/svn/commit-cmd.c:171
>>> #15 0x000000000042b351 in sub_main (exit_code=0x7ffffffddf3c, argc=5,
>>> argv=0x7ffffffde038, pool=0x7fffff6c0028)
>>>     at subversion/svn/svn.c:3041
>>> #16 0x000000000042b5ee in main (argc=5, argv=0x7ffffffde038) at
>>> subversion/svn/svn.c:3126
>>>

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